The present invention relates to an automatic control apparatus for wind-shield wipers, and more particularly to an electro-optical liquid detector assembly for the automatic control apparatus which is adapted to electro-optically detect an adherence condition of liquid such as raindrops on the exterior surface of a wind-shield of wheeled vehicles, airplanes, ships or the like so as to produce an electric control signal necessary for automatic control of a wind-shield wiper in dependence upon a result of the detection.
In general, a conventional electro-optical liquid detector assembly of this kind comprises a transparent substrate attached to a portion of the interior surface of a wind-shield where the exterior surface of the wind-shield is wiped by a wiper blade, a light emission element assembled within the substrate to emit luminous rays towards the wind-shield so as to cause multiple internal reflection of luminous rays in the wind-shield, a light receiving element assembled within the substrate to receive and detect the incident luminous rays reflected by the exterior surface of the wind-shield, and an electric control circuit connected to the light receiving element for producing an electric control signal in dependence upon an amount of the incident luminous rays detected by the light receiving element.
In mounting process of the liquid detector assembly on the interior surface of the wind-shield, a transparent liquid adhesive is utilized to adhere the substrate to the interior surface of the wind-shield and retain it in place. If a portion of the adhesive protrudes from the adherence surface of the substrate during the mounting process, the protruded adhesive has to be wiped away. Additionally, the substrate has to be held in place for a period of time until the adhesive coagulates, resulting in decrease of the working efficiency in the mounting process. If air bubbles are included in the coagulated adhesive, the luminous rays to and from the wind-shield will be diffused due to presence of the air bubbles, resulting in an error in detection of the luminous rays.